Brooke’s father, a younger son of the 9th Lord Cobham and twice MP for Kent, left him a third share of his lands under gavelkind.
Brooke was eager to obtain a seat in the first Jacobean Parliament to defend the family interests after the attainder of his cousin, the 11th Lord Cobham. At the general election of 1604 Sir John Holles*, whom he greatly admired, recommended him to Sir Percival Willoughby* for Tamworth in Staffordshire, but without success. He tried again in the following year when a seat fell vacant at Queenborough, in Kent. The borough was under the control of his ‘kinsman and old acquaintance’ Sir Edward Hoby*, who promised him ‘all the kindness I could show’, but in the event the place went to another.
Having retired from military service, Brooke, now a gentleman of the privy chamber, devoted his energies instead to colonial and commercial ventures. He may not have made use of the licence to travel which he was granted in 1609, but in the following year he set sail with Sir Thomas Roe* for Guiana, and he later encouraged Luke Fox in his search for the North-West Passage, though he himself did not join the Company.
In 1614 Brooke was returned for Gatton in Surrey on the interest of his distant kinsman, lord admiral Nottingham (Charles Howard†).
At the next general election Brooke was nominated by Suffolk’s son-in-law, Lord (William†) Knollys, for a seat at Oxford, where Knollys was high steward. He was named to ten committees, including those for privileges (5 Feb. 1621), the subsidy bill (7 Mar.) and for drafting a bill to prevent the export of ordnance (26 March).
In April 1626 Brooke and Russell made a last-ditch attempt to revive the alum project, and were supported by a royal Proclamation ‘for the better making of saltpetre’.
In 1632 Brooke joined with Theophilus Howard*, 2nd earl of Suffolk, and the lord chief justice, Sir Robert Heath*, to purchase an interest in a tin mine at Kentwyn, Cornwall.
